fix(root): enforce command deadlines while draining output

[wangtong10086]

Root commands can block before reaching their timeout because stdout is read to EOF before waitFor. A detached child that retains stdout can also keep an otherwise completed su command waiting.

Add a bounded process runner that drains available output while checking a monotonic deadline, caps retained output, preserves nonzero exit status, and closes streams on exit. Root scripts also run inside Android's timeout so the root shell has its own deadline. Root availability checks use the same runner. Command strings are omitted from failure logs, and generated scripts use owner-only read/write permissions.

Validation on this branch:

• :app:testPlaystoreDebugUnitTest --tests com.v2ray.ang.root.RootProcessRunnerTest
• :app:testPlaystoreDebugUnitTest — 85 tests passed.
• :app:compilePlaystoreDebugKotlin
• Android 16 / arm64: a probe loaded this exact runner implementation from an installed personal build. A silent command with a 150 ms deadline returned in 155 ms; inherited stdout returned in 11 ms; 1 MiB output retained 4096 bytes and returned in 129 ms; exit status 4 and stderr were preserved. A device timeout test prevented a child from writing a delayed marker after termination.

Not run: runtime checks on Android 7–15 and non-arm64 devices; those devices were unavailable. The runner avoids Process.waitFor(timeout, unit) to retain API 24–25 compatibility. The device probe validates command execution; it does not establish lifecycle correctness for the upstream root service as a whole.